Stretchable display device

ABSTRACT

A stretchable display device is disclosed, which is able to be operated with three states of a non-stretched state, a transition state and a stretched state, and the stretchable display device includes a stretchable substrate and a plurality of light emitting units. The plurality of the light emitting units are disposed on the stretchable substrate, and the plurality of the light emitting units are in a mode of ON or in a mode of OFF. The light emitting units being in the mode of ON are in a number of N1 while in the non-stretched state, the light emitting units being in the mode of ON are in a number of N2 while in the transition state, and the light emitting units being in the mode of ON are in a number of N3 while in the stretched state, wherein N3≥N2&gt;N1.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

The present disclosure relates to a display device, and moreparticularly to a stretchable display device.

2. Description of the Prior Art

In recent years, display devices have become more and more important invarious electronic applications, such as smart phones, tablets, notebookcomputers, e-book readers and wearable devices (e.g., smart watches).Electronic manufacturers keeps on researching and developing new typedisplay devices. Among these devices, the image quality of stretchabledisplay devices may become poor after stretching, so that manufacturersstill need to keeps on researching and developing for manufacturingstretchable display devices with maintained stable display performance.

SUMMARY OF THE DISCLOSURE

Some embodiments of the present disclosure provide a stretchable displaydevice, which is able to be operated with three states of anon-stretched state, a transition state and a stretched state. Thestretchable display device includes a stretchable substrate and aplurality of light emitting units. The plurality of the light emittingunits are disposed on the stretchable substrate, and the plurality ofthe light emitting units can be in a mode of ON or in a mode of OFF. Thelight emitting units being in the mode of ON are in a number of N1 whilein the non-stretched state, the light emitting units being in the modeof ON are in a number of N2 while in the transition state, and the lightemitting units being in the mode of ON are in a number of N3 while inthe stretched state, wherein N3≥N2>N1.

According to the stretchable display device of some embodiments of thepresent disclosure, since the number of the light emitting units in themode of ON changes in the non-stretched state, the transition state andthe stretched state, the image quality during the stretching process maybe improved. In another aspect, according to the present disclosure, thesense of difference of the stretched image may be minor by controllingthe number of light emitting units in the mode of ON.

These and other objectives of the present disclosure will no doubtbecome obvious to those of ordinary skill in the art after reading thefollowing detailed description of the embodiment that is illustrated inthe various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the operation of a stretchable displaydevice according to the present disclosure.

FIG. 2 is a partial enlargement top-view schematic diagram of astretchable display device in various states according to a firstembodiment of the present disclosure.

FIG. 3 is a partial enlargement schematic diagram of a stretchabledisplay device in various states according to a second embodiment of thepresent disclosure.

FIG. 4 and FIG. 5 are schematic diagrams of the relationship between thenumber of light emitting units being in the mode of ON and the increasedmultiple of stretching in the light emitting group according to thesecond embodiment of the present disclosure.

FIG. 6 is a schematic diagrams of the relationship between the PPImultiple and the increased multiple of stretching according to a thirdembodiment of the present disclosure.

FIG. 7 is a schematic diagram of the relationship between the number oflight emitting units being in the mode of ON and the stretchingdimension in the light emitting group according to a fourth embodimentof the present disclosure.

FIG. 8 is a partial schematic diagram of a stretchable display device invarious states according to the fourth embodiment of the presentdisclosure.

FIG. 9 is a schematic diagram of a stretchable display device in variousstates according to a fifth embodiment of the present disclosure.

DETAILED DESCRIPTION

The present disclosure may be understood by reference to the followingdetailed description, taken in conjunction with the drawings asdescribed below. It is noted that, for purposes of illustrative clarityand being easily understood by the readers, various drawings of thisdisclosure show a portion of the device, and certain elements in variousdrawings may not be drawn to scale. In addition, the number anddimension of each element shown in drawings are only illustrative andare not intended to limit the scope of the present disclosure.

Certain terms are used throughout the description and following claimsto refer to particular components. As one skilled in the art willunderstand, electronic equipment manufacturers may refer to a componentby different names. This document does not intend to distinguish betweencomponents that differ in name but not function. In the followingdescription and in the claims, the terms “include” and “comprise” areused in an open-ended fashion, and thus should be interpreted to mean“include, but not limited to . . . ”. When the terms “include”,“comprise” and/or “have” are used in the description of the presentdisclosure, the corresponding features, regions, steps, operationsand/or components would be pointed to existence, but not limited to theexistence or addition of one or more corresponding features, regions,steps, operations, components and/or combinations thereof. When acomponent is referred to as being “on” or “connected to” anothercomponent, it may be directly on or directly connected to the othercomponent, or intervening components may be presented (indirectcondition). In contrast, when a component is referred to as being“directly on” or “directly connected to” another component, there are nointervening components presented.

The terms “about”, “substantially”, “equal”, or “same” generally meanwithin 20% of a given value or range, or mean within 10%, 5%, 3%, 2%,1%, or 0.5% of a given value or range.

In the present disclosure, “stretched/stretchable” means that whenexternal pressure and/or external force is applied to an object, theobject may be deformed, and this deformation may include the variationin the area, length, width and/or curvature of the object in anydirection(s), but not limited herein. For example, the increase ordecrease in the length of an object may be “stretched/stretchable”according to the present disclosure.

It should be noted that the technical features in different embodimentsdescribed in the following can be replaced, recombined, or mixed withone another to constitute another embodiment without departing from thespirit of the present disclosure.

Please refer to FIG. 1 and FIG. 2. FIG. 1 is a schematic diagram of theoperation of a stretchable display device according to the presentdisclosure. FIG. 2 is a partial enlargement top-view schematic diagramof a stretchable display device in various states according to a firstembodiment of the present disclosure. As shown in FIG. 1, in the presentdisclosure, the stretchable display device 100 is able to be operatedwith three states of a non-stretched state I, a transition state II anda stretched state III. The non-stretched state I is a state that thestretchable display device 100 is not stretched, the stretched state IIIis a state after the stretchable display device 100 is stretched, andthe transition state II is a state between the non-stretched state I andthe stretched state III during the stretching process.

The stretchable display device 100 may be stretched along one directionor various directions (e.g., but not limited to one direction, twodirections or three-dimensional directions). The stretchable displaydevice 100 may be stretched from the non-stretched state I to thestretched state III through the transition state II, so that thedimension of the stretchable display device 100 in at least onedirection may be changed after stretching. FIG. 1 is an example that thestretchable display device 100 may be stretched along a first directionD1 and a second direction D2. In the non-stretched state I, thestretchable display device 100 may have a width W1 in the firstdirection D1 and a length H1 in the second direction D2. When thestretchable display device 100 is being stretched, the stretchabledisplay device 100 may go through the transition state II firstly, andat this time the width W2 and the length H2 of the stretchable displaydevice 100 may be stretched and increased continuously. Until thestretchable display device 100 enters the stretched state III, thestretchable display device 100 may have the stretched width W3 andlength H3. In some embodiments, the width relationship is W1<W2<W3, andthe length relationship is H1<H2<H3, but not limited herein. Forexample, in other embodiments, W2 may be equal to W3. In still otherembodiments, H2 may be equal to H3. It should be noted that the width W2and the length H2 may not be a single value or a constant respectively.Since the stretchable display device 100 may be continuously stretchedin the transition state II, the width W2 and the length H2 may have aspecific range respectively. In addition, the stretchable display device100 of the present disclosure is not limited to being stretched in aplane along the first direction D1 and/or the second direction D2, butmay further be stretched in a third direction D3 perpendicular to theD1-D2 plane, so the stretched stretchable display device 100 may furtherform a curved display device, with a protrudent shape for instance,wherein a pixel compensation may be provided according to the presentdisclosure.

Please refer to FIG. 2. FIG. 2 is a partial enlargement top-viewschematic diagram of a stretchable display device in various statesaccording to the first embodiment of the present disclosure, wherein thepartially enlarged portions in the non-stretched state I, the transitionstate II and the stretched state III may, for example, respectivelycorrespond to the portion RA1, portion RA2 and portion RA3 in FIG. 1,but not limited herein. The stretchable display device includes astretchable substrate 110 and a plurality of light emitting units 120,wherein the light emitting units 120 are disposed on the stretchablesubstrate 110. The light emitting units 120 may be in a mode of ON (alsoreferred to as an ON mode) or in a mode of OFF (also referred to as anOFF mode) respectively. The ON mode may indicate that the light emittingunit 120 receives signals and thus operates (e.g., generates light), andthe OFF mode may indicate that the light emitting unit 120 does notreceive signals and thus does not operate (e.g., does not generatelight), but not limited herein.

In some embodiments, the ON mode may indicate that the light emittingunit 120 receives signals and the gray scale is greater than a low grayscale (e.g., the low gray scale means that the light intensity is lessthan 20% of the light intensity of the highest gray scale image), andthe OFF mode may indicate that the light emitting unit 120 receivessignals and the gray scale is less than or equal to the low gray scale.For example, the gray-scale measurement method may include measuring thelight intensity of the output light emitted by the light emitting units120 in the gray scale image with a spectrometer, and then comparing themeasured light intensity with the light intensity of the highest grayscale of the same display device to confirm the gray scale, wherein theoutput light that is measured indicates the final exiting light of thedisplay device, which can be observable by the user. The light intensityof the gray scale image may be obtained by measuring the same number oflight emitting units 120.

For instance, one light emitting unit 120 may represent one pixel, andone pixel may include a plurality of sub-pixels, for example, includinga red sub-pixel, a green sub-pixel and a blue sub-pixel, or including ared sub-pixel, a green sub-pixel, a blue sub-pixel and a whitesub-pixel, but not limited herein. In some embodiments, one lightemitting unit 120 may also represent one sub-pixel.

The stretchable substrate 110 may include a plurality of material layersor films. For example, the stretchable substrate 110 may include asubstrate and an optional buffer layer. The substrate may includepolymer materials, such as polyimide (PI), polyethylene terephthalate(PET), any combinations of the materials mentioned above, or any othersuitable materials, such as elastic materials or stretchable materials.The stretchable substrate 110 may include pixel parts 110 a andconnecting parts 110 b. The pixel parts 110 a are used for disposing thelight emitting units 120, and the adjacent pixel parts 110 a are spacedapart from each other. The connecting parts 110 b are disposed betweenthe adjacent pixel parts 110 a and connected to two adjacent pixel parts110 a, so that a pitch exists between the adjacent pixel parts 110 a,e.g., a pitch S1 in the non-stretched state I. A gap may be formedbetween the adjacent pixel parts 110 a and the connecting parts 110 b,e.g., a gap GP1 in the non-stretched state I. The gap in FIG. 2 may havea cross-like shape, but not limited herein, and the gap may further haveother shapes. When the stretchable display device 100 is stretched fromthe non-stretched state I to the stretched state III, the stretchablesubstrate 110 may be stretched together, so that the length of theconnecting part 110 b may increase and the pitch between adjacent pixelparts 110 a may enlarge to become a pitch S3, and the gap may alsoincrease accordingly. For example, the gap GP2 and the pitch S2 betweenadjacent pixel parts 110 a in the transition state II may berespectively greater than the gap GP1 and the pitch S1 in thenon-stretched state I, and the gap GP3 and the pitch S3 in the stretchedstate III may be greater than the gap GP2 and the pitch S2 in thetransition state II. In the embodiment shown in FIG. 2, the dimension ofthe pixel parts 110 a does not increase with stretching during thestretching process, but in some embodiments, the dimension of the pixelparts 110 a may also change during the stretching process. Each of thelight emitting units 120 may be respectively disposed on a surface of apixel part 110 a, but the present disclosure is not limited herein, andthe number of the light emitting units 120 disposed on a pixel part 110a may be multiple.

According to the present disclosure, when the stretchable display device100 is in the non-stretched state I, only a portion of the plurality ofthe light emitting units 120 are in the mode of ON (shown by the squareframes without shading in FIG. 2). For example, in the non-stretchedstate I, the plurality of the light emitting units 120 in the ON modeare in a number of N1. In contrast, in the non-stretched state I,another portion of the plurality of the light emitting units 120 are inthe OFF mode (shown by the square frames with cross-diagonal shading inFIG. 2). During the stretching process, that is, when the stretchabledisplay device 100 is in the transition state II, the assisting lightemitting units 120 may switch from the OFF mode to the ON mode. That isto say, the number of the light emitting units 120 in the ON mode maybegin to change, so that the plurality of the light emitting units 120in the ON mode are in a number of N2, and the number N2 is greater thanthe number N1. After stretching, when the stretchable display device 100is in the stretched state III, the plurality of the light emitting units120 in the ON mode are in a number of N3, wherein the number N3 isgreater than or equal to the number N2, and the number N3 may be equalto or less than the total number of the light emitting units 120 on thestretchable substrate 110. That is to say, when the stretchable displaydevice 100 enters the stretched state III, for example (but not limitedto), all of the light emitting units 120 may be in the ON mode,alternatively, a portion of the light emitting units 120 may still be inthe OFF mode in some other embodiments. From the above description, therelationship between the number of the light emitting units 120 turnedon in different states is N3≥N2>N1. According to the present disclosure,by changing the assisting lighting emitting units 120 from the OFF modeto the ON mode, the image quality before and after stretching may beimproved or maintained.

Please refer to FIG. 1 and FIG. 2. When the stretchable display device100 is in the non-stretched state I, the stretchable substrate 110 has afirst area A1, and a number N1 of light emitting units 120 are in the ONmode, while the other light emitting units 120 are in the OFF mode. Inthe present disclosure, a number of the light emitting units 120 beingin the ON mode per unit area of the stretchable substrate 100 that isnon-stretched is defined as a first turned-on number of light emittingunits per unit area PPA_1 (i.e., the stretchable display device 100 hasa PPA_1 that is defined as a number of light emitting units 120 being inthe mode of ON per unit area of the stretchable substrate 110 while inthe non-stretched state I, and PPA_1=N1/A1). In the transition state IIwhile stretching, the stretchable substrate 110 may have a transitionarea At. After stretching, when the stretchable display device 100 is inthe stretched state III, the stretchable substrate 110 has a second areaA2. In this embodiment, for example, the first area A1 is less than thetransition area At, and the transition area At is less than the secondarea A2, but not limited herein. Compared with the non-stretched stateI, the assisting light emitting units 120 may change from the OFF modeto the ON mode in the stretched state III, and at this time, a number N3of light emitting units 120 are in the ON mode. In the presentdisclosure, a number of the light emitting units 120 being in the ONmode per unit area of the stretchable substrate 110 that is stretched isdefined as a second turned-on number of light emitting units per unitarea PPA_2 (i.e., the stretchable display device 100 has a PPA_2 that isdefined as a number of light emitting units 120 being in the mode of ONper unit area of the stretchable substrate 110 while in the stretchedstate III, and PPA_2=N3/A2), wherein the second area A2 is differentfrom the first area A1. As described above, the second area A2 isgreater than the first area A1, but not limited herein. According tosome embodiments of the present disclosure, the stretchable displaydevice 100 may be designed as making the second turned-on number oflight emitting units per unit area PPA_2 be substantially equal to (orgreater than or equal to) the first turned-on number of light emittingunits per unit area PPA_1, so that the image quality in the stretchedstate III may not be worse than the image quality in the non-stretchedstate I, but the present disclosure is not limited herein. According tosome embodiments, a turned-on number of light emitting units per unitarea PPA before and after stretching may be appropriately controlled.For example, 1.5×PPA_1≥PPA_2≥0.5×PPA_1, thus, the image quality beforeand after stretching may be maintained. According to some embodiments,when stretching in one-dimensional direction, a turned-on number oflight emitting units per unit length PPI before and after stretching maybe appropriately controlled, for example, 1.5×PPI_1≥PPI_2≥0.5×PPI_1, sothat the difference in resolution per unit area (or PPI) before andafter stretching may not be too great, and the image quality before andafter stretching may be maintained.

According to the present disclosure, among the plurality of the lightemitting units 120, a light emitting group may be formed of lightemitting units 120 with a number of Q. For example (but not limited to),a light emitting group may be composed of a number of two, three or fourlight emitting units 120, so as to form a plurality of light emittinggroups 122. According to some embodiments of the present disclosure, theratio of the second area A2 of the stretchable substrate 110 in thestretched state III to the first area A1 of the stretchable substrate110 in the non-stretched state I is defined as a ratio M (i.e., A2/A1),and the ratio M is less than or equal to Q (i.e., M≤Q), that is, themultiple of the second area A2 to the first area A1 may be less than orequal to the number of the light emitting units 120 in one lightemitting group 122. Through the above design, the second turned-onnumber of light emitting units per unit area PPA_2 may be greater thanor equal to the first turned-on number of light emitting units per unitarea PPA_1, so that at least the same value of the turned-on number oflight emitting units per unit area PPA may be maintained before andafter stretching, and the image quality may not be greatly affected dueto stretching. For example, the brightness per unit area may bemaintained. This design will be illustrated in detail in followingexamples.

Please refer to FIG. 2. In some embodiments, the stretchable displaydevice 100 includes a plurality of light emitting units 120, whereinfour light emitting units 120 form a group to form a plurality of lightemitting groups 122 (i.e., the number Q described above is 4). When thestretchable display device 100 is in the non-stretched state I, thestretchable substrate 110 has a first area A1, and in each of the lightemitting groups 122, one light emitting unit 120 is in the ON mode whilethe other three light emitting units 120 are in the OFF mode. Thus, thefirst turned-on number of light emitting units per unit area PPA_1 maybe obtained (four light emitting units divided by one time the area:4/1=4). When the stretchable substrate 110 is stretched to twice thelength along the horizontal first direction D1 and the vertical seconddirection D2 respectively, the stretchable display device 100 becomes tobe in the stretched state III, and the stretchable substrate 110 has asecond area A2, wherein the second area A2 is four times the first areaA1, and in each of the light emitting groups 122, the three lightemitting units 120 that were originally in the OFF mode become to be inthe ON mode, that is, the four light emitting units 120 are all in theON mode. Thus, the second turned-on number of light emitting units perunit area PPA_2 may be obtained (sixteen light emitting units divided byfour times the area: 16/4=4). According to the change of area and thechange of the number of the light emitting units 120 in the ON modebefore and after stretching, it can be understood that the secondturned-on number of light emitting units per unit area PPA_2 is equal tothe first turned-on number of light emitting units per unit area PPA_1,that is, the brightness per unit area is nearly unchanged. However, ifthe ratio of the second area A2 to the first area A1 is greater than thenumber Q of the light emitting units 120 forming a light emitting group122, that is, if (A2/A1)>4, the second turned-on number of lightemitting units per unit area PPA_2 may be less than the first turned-onnumber of light emitting units per unit area PPA_1. Therefore, when fourlight emitting units 120 form a group of the light emitting groups 122,the ratio of the second area A2 in the stretched state III to the firstarea A1 in the non-stretched state I may be designed as being less thanor equal to 4, that is, (A2/A1)≤4 (i.e., M≤Q), such that at leastidentical number of turned-on light emitting units per unit area may bemaintained before and after stretching, as mentioned in the previousparagraph.

According to some embodiments, during the stretching process, thestretchable display device 100 has a transition state II between thenon-stretched state I and the stretched state III, so the light emittingunits 120 that were originally in the OFF mode may be all turned on orpartially turned on in the transition state II. For example, the lightemitting units 120 may switch to be in the ON mode in succession beforeentering the stretched state III, and when the stretchable displaydevice 100 enters the stretched state III, all of the light emittingunits 120 become to be in the ON mode, but not limited herein.

As the description above, the number (N3) of the light emitting units inthe ON mode while the stretchable display device is in the stretchedstate is greater than the number (N1) of the light emitting units in theON mode while the stretchable display device is in the non-stretchedstate. According to some embodiments, a suitable threshold dimension maybe designed to determine a suitable time point for increasing the numberof the light emitting units in the ON mode or a suitable time forturning on further light emitting units. As shown in FIG. 1, thestretchable display device 100 may be stretched along a direction, e.g.along the first direction D1. While in the non-stretched state I, thedimension of the stretchable display device 100 in this direction isdefined as a minimum dimension Lmin, such as a width W1. In thestretched state III, the dimension of the stretchable display device 100in this direction is defined as a maximum dimension Lmax, such as awidth W3. When the dimension of the stretchable display device 100 inthis direction is less than a threshold dimension Lc1 (for example, whenthe dimension is the width W1), the number of the light emitting unitsin the ON mode is Y1, such as N1. The threshold dimension Lc1 is greaterthan the minimum dimension Lmin and less than the maximum dimensionLmax, that is, Lmin<Lc1<Lmax. When the dimension of the stretchabledisplay device 100 in this direction is greater than or equal to thethreshold dimension Lc1 (for example, when the dimension is the widthW2), the number of the light emitting units in the ON mode is N2,wherein N2 is greater than N1. In detail, the dimension of thestretchable display device 100 in this direction may be the length orthe width of the stretchable substrate 110 in this direction.

Please refer to FIG. 3. FIG. 3 is a partial enlargement schematicdiagram of a stretchable display device in various states according to asecond embodiment of the present disclosure. FIG. 3 illustrates that thestretchable display device 100 may be stretched in a single direction(e.g. the first direction D1) as an example. In the following thirdembodiment and fourth embodiment, the stretchable display device 100 isalso stretched in a single direction as an example, and will not beredundantly described, but the present disclosure is not limited herein.The suitable number and suitable time for turning on the light emittingunits 120 and related descriptions in FIG. 3 and other embodiments maybe modified and changed by those skilled in the art according to thedisclosure and experience, so as to obtain the design of the stretchabledisplay device 100 when stretching in multiple directions.

According to some embodiments of the present disclosure, according tothe relationship between the dimension of the stretchable display device100 in the direction and a threshold dimension, a suitable time forincreasing the number of the light emitting units in the ON mode may bedetermined through the suitable threshold dimension. The dimension ofthe stretchable display device 100 in one direction may be a pitch oftwo adjacent light emitting groups 122 in the direction.

For example, referring to FIG. 3, the stretchable display device 100includes a plurality of light emitting units 120, wherein a number Q(such as Q=2) of light emitting units 120 form a group to form aplurality of light emitting groups 122. When the stretchable displaydevice 100 is in the non-stretched state I, a pitch between adjacentlight emitting groups 122 is defined as a first dimension L1, and onelight emitting unit 120 is in the ON mode and another one light emittingunit 120 is in the OFF mode in each of the light emitting groups 122.For example, in each of the light emitting groups 122, the left lightemitting unit 120 is in the ON mode, but not limited herein. Indifferent embodiments, the right light emitting unit 120 in each of thelight emitting groups 122 may be turned on, or the light emitting units120 in the ON mode in different light emitting groups 122 may be indifferent positions, in other words, the positions of the turned-onlight emitting units 120 may not be completely the same. As shown inFIG. 3, when the stretchable substrate 110 is stretched along thehorizontal first direction D1, the stretchable display device 100 may gothrough the transition state II firstly. Furthermore, when thestretchable substrate 110 is stretched to twice the length, thestretchable display device 100 may enter the stretched state III. Atthis time, the pitch between the two adjacent light emitting groups 122becomes a second dimension L2, and the light emitting unit 120 that wasoriginally in the OFF mode has changed to be in the ON mode, that is,both of the light emitting units 120 are in the ON mode in each lightemitting group 122. The transition state II shown in FIG. 3 mayrepresent the turned-on time point of the second light-emitting unit 120in the light emitting group 122. In other words, when the stretchablesubstrate 110 is stretched until the pitch between two adjacent lightemitting groups 122 is the threshold dimension Lc1, the number of lightemitting units 120 in the ON mode starts to change, that is, theassisting light emitting units 120 begin to change from the OFF mode tothe ON mode, so that the number of light emitting units 120 in the ONmode in each of the light emitting groups 122 changes from one to two.

The design of the threshold dimension will be discussed below. Pleaserefer to FIG. 4 and FIG. 5 accompanied with FIG. 3, wherein FIG. 4 andFIG. 5 are schematic diagrams of the relationship between the number oflight emitting units being in the ON mode and the stretching dimensionin the light emitting group according to the second embodiment of thepresent disclosure. FIG. 4 and FIG. 5 respectively show differentconditions in the stretching process, wherein the stretching dimensionrefers to the pitch between adjacent light emitting groups 122 in thefirst direction D1 as an example, but not limited herein. The stretchingdimension in the embodiments of the present disclosure refers to thedimension of the stretchable display device 100. In differentembodiments of the present disclosure, the “dimension of the stretchabledisplay device” may refer to a dimension in one direction, or adimension in more than one direction. For example, the dimension of thestretchable display device may be the dimension of the light emittinggroup, the pitch between two adjacent light emitting groups, the lengthor width of the stretchable substrate, or the area of the stretchablesubstrate, but not limited herein.

Please refer to FIG. 3, FIG. 4 and FIG. 5. When the stretchable displaydevice 100 is in the non-stretched state I, the pitch between adjacentlight emitting groups 122 (referred as the stretching dimension below)is a first dimension L1, and the number of the light emitting units inthe ON mode in each of the light emitting groups 122 is U1, as shown bythe point Pon1, wherein U1 is 1 for example, but not limited herein.When the stretchable substrate 110 is stretched along the horizontalfirst direction D1 to have a second dimension L2, the stretchabledisplay device 100 becomes the stretched state III, and the number ofthe light emitting units in the ON mode in each of the light emittinggroups 122 is U2, as shown by the point Pon2, wherein U2 is 2 forexample, but not limited herein. In the embodiment shown in FIG. 3, thesecond dimension L2 is twice the first dimension L1 as an example, butnot limited herein. The transition state II between the non-stretchedstate I and the stretched state III represents that the stretchingdimension of the stretchable substrate 110 is greater than the firstdimension L1 and less than the second dimension L2. Furthermore, in thetransition state II, when the stretchable substrate 110 is stretched toreach the threshold dimension Lc1, the assisting light emitting units120 may start to change from the OFF mode to the ON mode. In otherwords, the number of the light emitting units 120 in the ON mode is U2in one light emitting group 122, as shown by the point Ponc.

As shown in FIG. 4 and FIG. 5, the horizontal axis is the increasedmultiple of stretching, and the vertical axis is the number of the lightemitting units 120 turned on in one light emitting group 122. In thehorizontal axis, the position symbolized with “0” represents theincreased multiple of dimension of the stretchable substrate 110 in thenon-stretched state I, and at this time, the stretchable substrate 110has not been stretched to increase its dimension, so the increasedmultiple of stretching is 0. In other words, the stretching dimension ofthe stretchable substrate 110 is the first dimension L1 in thenon-stretched state I. The position symbolized with “1” represents theincreased multiple of dimension of the stretchable substrate 110 in thestretched state III, wherein the dimension of the stretchable substrate110 is doubled, that is, the dimension of the stretchable substrate 110becomes the second dimension L2. The position symbolized as 1/nrepresents that the length is increased by 1/n times, that is, thedimension of (1/n)×L1 is increased. The position symbolized with n−1/nrepresents that the length is increased by n−1/n times, that is, thedimension of (n×1/n)×L1 is increased. In other words, the minimum unitof the increased multiple of stretching is set as 1/n (i.e., thedimension increased by stretching is (1/n)×L1), wherein “n” is anextremely large number. That is to say, assumed that between the firstdimension L1 in the non-stretched state I (being stretched zero times)and the second dimension L2 in the stretched state III (after beingstretched doubled), it is divided into “n” equal parts, and “1/n”represents that a length of 1/n times the first dimension L1 isincreased, but the present disclosure is not limited herein. Asdescribed above, when the increased multiple of stretching is k/n, theslope SL is calculated as

${PPI}_{\frac{k}{n}} - {{PPI}_{\frac{k - 1}{n}}.}$Furthermore, when the increased multiple of stretching is p/n and thestretchable substrate 110 has the threshold dimension Lc1, the assistinglight emitting units 120 may change from the OFF mode to the ON mode,such that the number of the light emitting units 120 in the ON mode ineach of the light emitting groups 122 may change from one (U1) to two(U2). Therefore, if a number of the light emitting units 120 being inthe ON mode per unit length is defined as “a turned-on number of lightemitting units per unit length PPI”, the calculation method of theturned-on number of light emitting units per unit length PPI and theslope SL may can be divided into two conditions when the increasedmultiple of stretching is k/n:

-   (1) As shown in FIG. 4, when p≤k, two light emitting units 120 are    in the ON mode in each of the light emitting groups 122, e.g., the    point Ponk. Therefore, the turned-on number of light emitting units    per unit length is

${{PPI}_{\frac{k}{n}} = {\frac{2}{1 + \frac{k}{n}} = \frac{2 \times n}{n + k}}},$and the slope is

${SL}_{\frac{k}{n}} = {{{PPI}_{\frac{k}{n}} - {PPI}_{\frac{k - 1}{n}}} = {\frac{2 \times n}{n + k} - \frac{2 \times n}{n + k - 1}}}$

-   (2) As shown in FIG. 5, when p>k, one light emitting unit 120 is in    the ON mode and another light emitting unit 120 is in the OFF mode    in each of the light emitting groups 122, e.g., the point Ponk. The    turned-on number of light emitting units per unit length is

${{PPI}_{\frac{k}{n}} = {\frac{1}{1 + \frac{k}{n}} = \frac{n}{n + k}}},$and the slope is

${SL}_{\frac{k}{n}} = {{{PPI}_{\frac{k}{n}} - {PPI}_{\frac{k - 1}{n}}} = {\frac{n}{n + k} - {\frac{n}{n + k - 1}.}}}$

Since the condition that p=k occurs only once in the stretching processand “n” is a extremely large number, the influence is very small andneglectable. When the p value is smaller, the number of occurrences ofthe condition (1) is greater, the number of occurrences of the condition(2) is smaller, and the slope in the condition (1) is twice the slope inthe condition (2). Thus, when the p value is smaller, the variation inthe slope of the curve is greater (e.g., the value that the slope ofeach point on the curve (of the turned-on number of light emitting unitsper unit length PPI to the stretching dimension, PPI-dimension curve)are squared and then summed is greater), such that the sense ofdifference of the stretching image are greater. Therefore, in thestretching process, the earlier the time point at which the number ofthe light emitting units 120 in the ON mode starts to change, thegreater the sense of difference of the stretching image. From the abovedescription, the p value should not be too small, for example, shouldnot be extremely close to the first size L1.

In some embodiments, as shown in FIG. 3 and FIG. 4, the first dimensionL1 may be a minimum dimension Lmin of the stretchable display device 100(or the stretchable substrate 110) in the first direction D1 (thedimension herein is the length as an example, not redundantlydescribed), and the second dimension L2 may be a maximum dimension Lmaxof the stretchable display device 100 (or the stretchable substrate 110)in the first direction D1. When the dimension of the stretchable displaydevice 100 in the first direction D1 is less than the thresholddimension Lc1, the number of the light emitting units 120 in the ON modein one light emitting group is U1, and when the dimension of thestretchable display device 100 in the first direction D1 is greater thanor equal to the threshold dimension Lc1, the number of the lightemitting units 120 in the ON mode in one light emitting group is U2,wherein the number U2 is greater than the number U1, both of the numberU2 and the number U1 are positive integers, and the threshold dimensionLc1 is greater than the minimum dimension Lmin and less than the maximumdimension Lmax. In some embodiments, the number U2 is the number of alllight emitting units 120 in one light emitting group 122. In someembodiments, the number U2 is less than the total number of the lightemitting units 120 in one light emitting group 122. In some embodiments,when the stretchable display device 100 has the maximum dimension Lmaxin the first direction D1, all of the light emitting units 120 in onelight emitting group 122 are in the ON mode. In some embodiments, thethreshold dimension Lc1 is in a range from (Lmin+Lmax)/3 to(Lmin+Lmax)/2, that is, (Lmin+Lmax)/3≤Lc1≤(Lmin+Lmax)/2, but not limitedherein.

Please refer to FIG. 6. FIG. 6 is a schematic diagrams of therelationship between the PPI multiple and the increased multiple ofstretching according to a third embodiment of the present disclosure. InFIG. 6, the stretching dimension (stretching length) from X to 2X isdivided into 128 units, and simulating is performed by increasing thedimension by X/128 every time to obtain data. For example, one lightemitting group includes two light emitting units. The “0” in thehorizontal axis represents that the increased multiple of stretching iszero, that is, the length without stretching is X, the scale “128/128”represents that the one time of the length is increased (i.e., theincreased multiple of stretching is 1, or the length is doubled) and thelength is 2X, and the scale “64” represents that it is stretched toincrease the dimension (length) of 64X/128, that is, it is stretched toincrease 0.5*X. In the state that the length is equal to X, when thenumber of light emitting units 120 in the on mode in the light emittinggroup 122 is set to 1, the turned-on number of light emitting units perunit length PPI is 1/X, and the PPI multiple is defined as 1, as shownat point A in FIG. 6.

In the stretching process, if no assisting light emitting unit 120changes from the OFF mode to the ON mode, the turned-on number of lightemitting units per unit length PPI may decrease continuously as thestretching length increases. For example, when the increased multiple ofstretching is 1 (i.e., the dimension is doubled), the turned-on numberof light emitting units per unit length PPI may decrease to half of theoriginal one (PPI multiple changes from 1 to 0.5), thereby reducing theimage quality, as shown by the line segment ABCD. In contrast, if thereare assisting light emitting units 120 changing from the OFF mode to theON mode in the stretching process, the turned-on number of lightemitting units per unit length PPI may increase when the assisting lightemitting units 120 are turned on, and then slowly decrease withstretching to the stretched state III to maintain the PPI multiple valueas 1. In this design, the value of the turned-on number of lightemitting units per unit length PPI may be maintained approximately equalbefore and after stretching, so as to provide more consistent imagequality. According to some embodiments, the range of the multiple of theturned-on number of light emitting units per unit length PPI before andafter stretching may be controlled between 0.5 and 1.5, that is,1.5×PPI_1≥PPI_2≥0.5×PPI_1. Similarly, when stretching in two dimensionaldirections, the range of the turned-on number of light emitting unitsper unit area PPA before and after stretching should be controlledbetween 0.5 and 1.5, that is, 1.5×PPA_1≥PPA_2≥0.5×PPA_1, so as tomaintain the image quality before and after stretching.

When the number of light emitting units 120 in the ON mode changes, itmay affect the display image, such as generating a sense of difference.According to some embodiments, in order to reduce the sense ofdifference of the display image, a suitable threshold dimension may bedesigned. The setting of the threshold dimension is discussed below.Please refer to FIG. 6, for example, in the state that the length is 2X,the number of light emitting units 120 in the ON mode in the lightemitting group 122 are increased. For example, the number is increasedto 2. Therefore, in the state that the length is 2X, the PPI is 2/2X, soPPI multiple is also equal to 1, as shown at the point H in FIG. 6. Whenthe time point that the number of light emitting units 120 in the ONmode starts to change is earlier, that is, when the threshold dimensionLc1 is very small or close to the non-stretched dimension X, the curveof the turned-on number of light emitting units per unit length PPImultiple to the dimension (PPI-dimension Curve) may be, for example, aline segment AEFGH, and the slope of the curve changes greatly in theinterval DP1, which makes the sense of difference of the display imagegreat. In contrast, when the time point that the number of lightemitting units 120 in the ON mode starts to change is later, that is,when the threshold dimension Lc1 is very large or close to the stretcheddimension 2X, the curve of the turned-on number of light emitting unitsper unit length PPI multiple to the dimension may be, for example, aline segment ABCDH, wherein the multiple of the turned-on number oflight emitting units per unit length PPI is low before the point D ofthe interval DP2, so that the image quality is poor. Consideringcomprehensively the influence of the time point when the number of thelight emitting units 120 in the ON mode starts to change on the sense ofdifference of the stretched image and the influence of the turned-onnumber of light emitting units per unit length PPI on the image quality,and considering that the range of the turned-on number of light emittingunits per unit length PPI before and after stretching should becontrolled between 0.5 and 1.5, the threshold dimension may be set inthe interval range between the stretching increase unit corresponding tothe point F (i.e., the curve is a line segment ABFGH) and the point G(i.e., the curve is a line segment ABCGH), that is, the interval DP3.Thus, the change amount of the slope of the curve may be small, and theturned-on number of light emitting units per unit length PPI in thetransition state II may be greater than or equal to the first turned-onnumber of light emitting units per unit length PPI_I of in thenon-stretched state I, so that the sense of difference of the displayimage during stretching is small and the image quality is high. Indetail, in the line segment ABFGH, the assisting light emitting units120 may change from the OFF mode to the ON mode when the multipleincreased by stretching is ⅓ (or the stretching dimension increases by42X/128). In the line segment ABCGH, the assisting light emitting units120 may change from the OFF mode to the ON mode when the multipleincreased by stretching is ½ (or the stretching dimension increases by64X/128). Therefore, the range of the threshold dimension Lc1 may bedesigned within the interval that the length is stretched and increasedby 0.33 times to 0.5 times (i.e., the dimension is within the intervalbetween 1.33X to 1.5X), that is, 1.33×≤Lc1≤1.5×. Thus, the sense ofdifference of the stretched image is small and the image quality ishigh.

Please refer to FIG. 7 and FIG. 8. FIG. 7 is a schematic diagram of therelationship between the number of light emitting units being in themode of ON and the stretching dimension in the light emitting groupaccording to a fourth embodiment of the present disclosure. FIG. 8 is apartial schematic diagram of a stretchable display device in variousstates according to the fourth embodiment of the present disclosure. Insome embodiments, the stretchable display device 100 includes aplurality of light emitting units 120, one light emitting group 122includes three light emitting units 120, and the stretchable substrate110 may be stretched to three times the length. FIG. 8 only shows onelight emitting group 122 as an example, but the present disclosure isnot limited herein. In other embodiments, one light emitting group 122may include other numbers of light emitting units 120. In someembodiments, each of the light emitting units 120 may include aplurality of sub-pixels or a plurality of light emitting elements. Forexample, one light emitting unit 120 includes three light emittingelements 1201, 1202 and 1203 side by side, which may represent threesub-pixels respectively, such as (but not limited to) a red sub-pixel, agreen sub-pixel and a blue sub-pixel. When the stretchable displaydevice 100 is in the non-stretched state I, the stretchable substrate110 has a first dimension L1 (the horizontal coordinate is X), and thenumber of the light emitting units 120 in the ON mode in each of thelight emitting groups 122 is U1, and the number U1 is 1 for example.When the stretchable substrate 110 is stretched to the stretched stateIII along the horizontal first direction D1, the stretchable substrate110 has a second dimension L2 (the horizontal coordinate is 3X, and thestretching dimension is increased by two times), that is, it isstretched from one time the length X of the original dimension to threetimes the length 3X, and the number of the light emitting units 120 inthe ON mode in each of the light emitting groups 122 is U3, and thenumber U3 is 3 for example. In the stretching process, a transitionstate II exists between the non-stretched state I and the stretchedstate III, wherein the assisting light emitting units 120 may changefrom the OFF mode to the ON mode respectively when the stretchablesubstrate 110 has the first threshold dimension Lc1 and the secondthreshold dimension Lc2. In detail, when the stretchable substrate 110is stretched to have the first threshold dimension Lc1, the number ofthe light emitting units 120 in the ON mode in each of the lightemitting groups 122 is U2, and the number U2 is 2 for example. Preciselyspeaking, a second light emitting unit 120 may change from the OFF modeto the ON mode (i.e. in one light emitting group 122, two light emittingunits 120 are in the ON mode and the other one light emitting unit 120is in the OFF mode). According to some embodiments, when the range ofthe first threshold dimension Lc1 is within the interval that the lengthis stretched and increased by 0.33 times to 0.5 times, that is,1.33×≤Lc1≤1.5×, the sense of difference of the stretched image may besmall and the image quality may be high. When the stretchable substrate110 is stretched to have the second threshold dimension Lc2, the numberof the light emitting units 120 in the ON mode in each of the lightemitting groups 122 is U3, and the number U3 is 3 for example, whereinU3>U2>U1. In detail, the third light emitting unit 120 of each of thelight emitting groups 122 may change from the OFF mode to the ON mode(i.e., all of the three light emitting units 120 in one light emittinggroup 122 are in the ON mode). According to some embodiments, when therange of the second threshold dimension Lc2 is within the interval thatthe length is stretched and increased by 1.33 times to 1.5 times, thatis, 2.33×≤Lc2≤2.5×, the sense of difference of the stretched image maybe small and the image quality may be high.

From the embodiments describe above, the rules of designing thethreshold dimension in some embodiments of the present disclosure may besummarized as follows. For example, in some embodiments, the stretchabledisplay device 100 includes a plurality of light emitting units 120,wherein a number Q of light emitting units 120 form a group to form aplurality of light emitting groups 122, and the stretchable substrate110 may be stretched to m times the length (i.e., the length isincreased by m−1 times). When the stretchable display device 100 is inthe non-stretched state I, the stretchable substrate 110 has a firstdimension L1, and one light emitting unit 120 is in the ON mode in eachof the light emitting groups 122. When the stretchable substrate 110 isstretched along the horizontal first direction D1 to m times the lengthto make the stretchable display device 100 be in the stretched stateIII, the stretchable substrate 110 has a second dimension L2, and thenumber of the light emitting units 120 in the ON mode in each of thelight emitting groups 122 is Q. In the stretching process, a transitionstate II exists between the non-stretched state I and the stretchedstate III. The stretchable substrate 110 may have a threshold dimensionLc_((Q-1)), which means that before the stretchable substrate 110 isstretched to the threshold dimension Lc_((Q-1)), only Q−1 light-emittingunits 120 in one light emitting group are in the ON mode, and one lightemitting unit 120 in one light emitting group is in the OFF mode.Furthermore, when the stretchable substrate 110 is stretched to thethreshold dimension Lc_((Q-1)), the Q^(th) light emitting unit 120(i.e., the last one light emitting unit 120 that has not been turned on)may change from the OFF mode to the ON mode. From the above description,the range of the threshold dimension Lc_((Qc-1)) may be set within theinterval that the stretching length is increased by (Q−2)+0.33 times to(Q−2)+0.5 times, that is, when (Q−2)+0.33≤the stretching multiplecorresponding to Lc_(Q-1)≤(Q−2)+0.5 or((Q−1)+0.33)×L1≤Lc_(Q-1)≤((Q−1)+0.5)×L1, the sense of difference of thestretched image may be small and the image quality may be high. Forexample, specifically, as shown in FIG. 7 and FIG. 8, Q=3, and the rangeof Lc_((Q-1)) (i.e., the second threshold dimension Lc2) may be designedas between [(Q−2)+1+0.33] times and [(Q−2)+1+0.5] times of the firstdimension L1 in the non-stretched state, that is, between 2.33×L1 and2.5×L1.

Please refer to FIG. 8. The change of turned-on positions of the lightemitting units 120 from the non-stretched state I through the transitionstate II to the stretched state III is introduced below. In thenon-stretched state I, one light emitting unit 120 in the light emittinggroup 122 is in the in mode ON. For example, the light emitting unit 120in the middle is in the ON mode, and the light emitting units 120 on twosides are in the OFF mode. In the transition state II during thestretching process, when the stretchable substrate 110 is stretched tothe first threshold dimension Lc1, one light emitting unit 120 that isturned on may be increased in the light-emitting unit group 122. Forexample, the second light emitting unit 120 in the light emitting group122 may change from the OFF mode to the ON mode. At this time, it can bedesigned to change the light emitting unit 120 disposed in the middlefrom the ON mode to the OFF mode, and change the two light emittingunits 120 disposed on two sides from the OFF mode to the ON mode, so asto obtain uniform image quality. Furthermore, when the stretchablesubstrate 110 is stretched to the second threshold dimension Lc2 orenters the stretched state III, all of the three light emitting units120 in the light emitting group 122 are in the ON mode, that is, themiddle light emitting unit 120 in the light emitting group 122 is alsoturned on. From the above description, in the stretching process, thelight emitting units 120 that are turned on may be changed whenstretching to the threshold dimension and requiring turning on theassisting number of light emitting units 120. For example, the lightemitting units 120 that are turned on may be changed according to thedisposing position of each of the light emitting units 120 in the lightemitting group 122, so that the distribution position of the turned-onlight emitting units 120 may be even, so as to make the image brightnessuniform and improve the image quality. For example, when stretching tothe threshold dimension, the light emitting units 120 that wereoriginally turned on may be turned off and meanwhile other lightemitting units 120 that were not originally turned on may be turned on,so that the positions of the turned-on light emitting units 120 areeven, and the brightness is uniform.

Please refer to FIG. 9. FIG. 9 is a schematic diagram of a stretchabledisplay device in various states according to a fifth embodiment of thepresent disclosure. In some embodiments, the overall brightness(candela/dimension²) of the image may also be adjusted or maintained byproviding different voltages or currents before and after stretching.For example, when the stretchable display device 100 is in thenon-stretched state I, the stretchable display device 100 has a firstarea A1, and the plurality of the light emitting units 120 have a firstbrightness C1. After stretching, when the stretchable display device 100is in the stretched state III, the stretchable display device 100 has asecond area A2, and the plurality of the light emitting units 120 have asecond brightness C2, wherein the second area A2 is greater than thefirst area A1, and the second brightness C2 is greater than the firstbrightness C1. By increasing the brightness of the light emitting unit120, after the stretchable display device 100 is stretched and the areathereof is changed, the overall image may be maintained to havesubstantially identical brightness per unit area before and afterstretching. The above-described method of adjusting the light emittingunits 120 may be, for example, increasing the brightness of the lightemitting elements by increasing the supply voltage or current thereof.In other embodiments, the overall brightness of the image before andafter stretching may also be adjusted or maintained through changing theplurality of the light emitting units 120 from the OFF mode to the ONmode by regions. For example, when the stretchable display device 100 isin the non-stretched state I, the stretchable display device 100 has afirst area A1, and only the light emitting units 120 in a few regionsamong the plurality of the light emitting units 120 are in the ON mode.After stretching, when the stretchable display device 100 is in thestretched state III, the stretchable display device 100 has a secondarea A2, and the light emitting units 120 in more or all regions amongthe plurality of the light emitting units 120 may all be in the ON mode,so as to maintain overall image with equal brightness before and afterstretching, but not limited herein.

In some embodiments, when there is no need to display the image duringthe stretching process (i.e., in the transition state II), the image maynot be displayed during the stretching process, and the image may bedisplayed after the stretching is completed to enter the stretched stateIII. For example, the stretchable display device 100 includes aplurality of light emitting units 120, wherein a number of Q of lightemitting units 120 form a group to form a plurality of light emittinggroups 122. When the stretchable display device 100 is in thenon-stretched state I, the stretchable display device 100 has a firstarea A1, and the number of the light emitting units 120 being in the ONmode per unit area of the stretchable substrate 110 that is notstretched is defined as a first turned-on number of light emitting unitsper unit area PPA_1. After stretching, when the stretchable displaydevice 100 is in the stretched state III, the stretchable display device100 has a second area A2, and the number of the light emitting units 120being in the ON mode per unit area of the stretchable substrate 110 thatis stretched is defined as a second turned-on number of light emittingunits per unit area PPA_2, wherein the second area A2 is different fromthe first area A1. For example, the second area A2 is greater than thefirst area A1, but not limited herein. Furthermore, the first turned-onnumber of light emitting units per unit area PPA_1 is equal to thesecond turned-on number of light emitting units per unit area PPA_2.During the stretching process, that is, in the transition state II, whenthe ratio of the second area A2 in the stretched state III to the firstarea A1 in the non-stretched state I divided by Q is not an integer(i.e., (A2/A1)/Q is not an integer), the image may not be displayed.When (A2/A1)/Q is an integer, the image may be displayed, and at thistime the turned-on number of light emitting units per unit area (PPA) orthe turned-on number of the turned-on number of light emitting units perunit length (PPI) may be maintained substantially the same.Alternatively, until the stretching is completed, i.e., when thestretched state III is reached, or when the first turned-on number oflight emitting units per unit area PPA_1 is equal to the secondturned-on number of light emitting units per unit area PPA_2, the imageis displayed. Thus, the image is discontinuous during the stretchingprocess.

According to some embodiments of the present disclosure, when thestretchable display device is in the non-stretched state, the transitionstate and the stretched state, the number of the light emitting units inthe mode of ON may change, so the image quality during the stretchingprocess may be adjusted. According to some embodiments, the displayimage of the stretchable display device in the stretched state and thenon-stretched state may maintain substantially the same turned-on numberof light emitting units per unit area, turned-on number of lightemitting units per unit dimension/length and/or brightness per unitarea, and this design, for example, may mitigate the deterioration ofthe image quality after stretching. In addition, according to someembodiments, designing suitable threshold dimensions may make the senseof difference of the stretched image small and improve the variabilityof the display image in the stretching process.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the disclosure. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A stretchable display device, which is able to beoperated with three states of a non-stretched state, a transition stateand a stretched state, wherein the non-stretched state is a state thatthe stretchable display device is not stretched, the stretched state isa state after the stretchable display device is stretched, and thetransition state is a state between the non-stretched state and thestretched state during a stretching process of the stretchable displaydevice, the stretchable display device comprising: a stretchablesubstrate; and a plurality of light emitting units disposed on thestretchable substrate, wherein the plurality of the light emitting unitscan be in a mode of ON or in a mode of OFF, the light emitting unitsbeing in the mode of ON in a number of N1 while in the non-stretchedstate, the light emitting units being in the mode of ON in a number ofN2 while in the transition state, and the light emitting units being inthe mode of ON in a number of N3 while in the stretched state; whereinN3≥N2>N1.
 2. The stretchable display device of claim 1, having a PPA_1that is defined as a number of the plurality of the light emitting unitsbeing in the mode of ON per unit area of the stretchable substrate whilein the non-stretched state, and a PPA_2 that is defined as a number ofthe plurality of the light emitting units being in the mode of ON perunit area of the stretchable substrate while in the stretched state,wherein the PPA_2 is equal to the PPA_1.
 3. The stretchable displaydevice of claim 1, wherein all of the plurality of the light emittingunits are in the mode of ON while in the stretched state.
 4. Thestretchable display device of claim 1, wherein only a portion of theplurality of the light emitting units are in the mode of ON while in thestretched state.
 5. A stretchable display device, which is able to beoperated with three states of a non-stretched state, a transition stateand a stretched state, wherein the non-stretched state is a state thatthe stretchable display device is not stretched, the stretched state isa state after the stretchable display device is stretched, and thetransition state is a state between the non-stretched state and thestretched state during a stretching process of the stretchable displaydevice, the stretchable display device comprising: a stretchablesubstrate; and a plurality of light emitting units disposed on thestretchable substrate, wherein the plurality of the light emitting unitscan be in a mode of ON or in a mode of OFF, the light emitting unitsbeing in the mode of ON in a number of N1 while in the non-stretchedstate, the light emitting units being in the mode of ON in a number ofN2 while in the transition state, and the light emitting units being inthe mode of ON in a number of N3 while in the stretched state; whereinN3≥N2>N1, and wherein the stretchable display device has a PPA_1 that isdefined as a number of the plurality of the light emitting units beingin the mode of ON per unit area of the stretchable substrate while inthe non-stretched state, and a PPA_2 that is defined as a number of theplurality of the light emitting units being in the mode of ON per unitarea of the stretchable substrate while in the stretched state, wherein1.5×PPA_1≥PPA_2≥0.5×PPA_1.
 6. The stretchable display device of claim 5,wherein the PPA_2 is equal to the PPA_1.
 7. The stretchable displaydevice of claim 5, wherein all of the plurality of the light emittingunits are in the mode of ON while in the stretched state.
 8. Thestretchable display device of claim 5, wherein only a portion of theplurality of the light emitting units are in the mode of ON while in thestretched state.